Elon-- That friction you are measuring is mostly drag from the shaft seal, a
little bearing friction and some friction from liquid shearing due to
viscosity at the pumping temperature. That will not increase a whole lot
with speed; certainly not by a square function especially with racing motor
oils at temperatures in the 180-200 degree range. At 80psi output roughly 90
percent of the hp to pump the oil will be what goes into building the
pressure. The formula I gave in the other thread on hydraulic hybrids
applies here. Fluid power is psi x gpm /1714 = hp. Divide that by about
.85 (which factor allows for the inefficiency in the pump drive belts) and
you'll get the horsepower use of the dry sump pressure pump stage. As far
as the scavenge pump stages are concerned they will be pumping the same
amount only to a somewhat lower pressure. If you know that pressure then
use the same formula and reduce figure that dividing constant of 0.85 will
be about 1.0 minus 0.08 x the number of scavenge stages (eg 0.76 for 3
scavenge stages.) Air entrained in the scavenge pump flow will not have a
big effect on the total horsepower once the motor is up to speed and the pan
has been "emptied" of residual oil that was there when the engine fired up.
My numbers on this come from data I accumulated on the performance of small
industrial gear pumps in my 1st job with Worthington pump 40 years ago. It's
a subject I feel I'm fairly well versed in. (& I don't throw away very
much). For anyone really that interested in the minutia of the subject I
will be glad to copy and forward (snail mail or email) what you may be
interested in. (lots of charts and pump performance curves.)
Still, if anyone out there has seen actual test stand performance on
multistage dry sump pumps, especially horsepower readings from calibrated
electric drives I'd love to look at it and use it to refine the constants in
my abovementioned formulas.
Ed
----- Original Message -----
From: "Elon" <saltfever@comcast.net>
To: "land-speed submit" <land-speed@autox.team.net>
Sent: Friday, January 02, 2009 4:55 PM
Subject: [Land-speed] Dry Sump
> Skip, after you raised the question I went out and put a torque wrench my
4
> stage, Moroso, gerotor pump. The problem with quantifying ''dry sump'' is
> there are too many variables. HP will vary with, number of stages, oil
> viscosity, oil pressure, and gear type (spur vs. gerotor). Anyway, I put
a
> torque wrench on it and got 14 inch ounces (with residual internal oil but
> not flowing oil). That seems quite high but I guess that is it's internal
> friction. If I had a torque sensor I could pump oil by using a hand drill
.
> . .sorry. So if friction increases as the square of the speed (I forget);
14
> in-oz (or .07lb-ft) at 5252rpm is about 5 hp in friction alone. -Elon
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